Electrical discharge device



April 16, 1935. E. F. LOWRY ELECTRICAL DISCHARGE DEVICE Filed Nov. 16,1929 lNVENTOR Erwin F? Lowry.

ATTORNEY Patented Apr. 16, 1935 PATENT OFFICE ELECTRICAL DISCHARGEDEVICE Erwin F. Lowry, Forest ,Hills, Pa., assignor to WestinghouseElectric & ManufacturingCompany, a corporation of PennsylvaniaApplication November 16, 1929, SerialNo. 407,690

1 Claim. (01. 250-27.5)

. surface.

Another object of my invention is to provide an electron-emissivecathode in which the ratio of the electron emission to theheatdissipation, by unit area of the cathode, is relativelylarge.

Another object of my invention is to provide an electrical-dischargedevice with an electronemissive cathode in which the rate ofheat'dissipation per unit area of surface, at a given operatingtemperature, isminimized.

A further object of my invention is to'provide an electron-emissivecathode for electrical-discharge devices which shall havea largersurface area than cathodesof the prior art but which shall be strong andrigidly mountedl Other objects of my invention will become apparent uponreading the following specification, taken in connection with thedrawing, in which Figure 1 is a view, in elevation, of anelectrical-discharge device having an electron-emissive cathodeembodying one form of my invention, and Fig. 2 is a sectional view takenon the line 11-11 of the tube shown in Fig. 1.

Fig. 3 is a view, in elevation, of another form of electron-emissivecathode of my invention.

Fig. 4 is a sectional View takenonthe line IV--IV of the tube shown inFig. 3.

o It is desirable, for certain, purposes, to provideelectrical-discharge devices with electron-emissive cathodes havingrelatively large surfaces and consequently capable of emittinglargeelectron currents. Such cathodes. are. desirable both for high-vacuumelectrical-discharge tubes and for electrical-discharge devices havinggaseous atmospheres at appreciable pressures. Devices in which mercuryvapor is present, as an atmosphere, about thecathode' are examplesof thelatter type. of .devices. However, when it is attempted to ensure alarge electron current by extending the surface area of the cathode tolarge dimensions, the energy'dissipated as heat from the cathode surface[becomes a serious source of loss and decreasedelectrical efficiency.One of the principal objects of my invention has been, accordingly, todevise methods of constructing hot cathodes which shall have relativelyextensive surface areas but which shall require only moderate amounts ofpower to maintain them at their proper operating temperatures Theforegoing objectI achieve by constructing the cathode of a relativelythin sheet material which is so bent back and forth or pleated that alarge fraction of its surface is so positioned that it.faces otherportions of its surface, In this way, the heat radiated from thefirst-mentioned portion of surface is absorbed by some other portion ofthe surface, and the amount dissipated to the surrounding surfaces andlost entirely is relatively small. Thus, the heating current has tosupply only the relatively small losses last mentioned, and the amountof cathode heating power required to maintain the cathode at itsoperating temperature is minimized.

It is, of course, necessary to devise a structure for the cathode whichshall be sufiiciently strong and rigid to maintain its shape, even whenheated to high temperatures, andthe' cathode structures which I describeherein have been found to be satisfactory in this regard.

With the foregoing principles and purposes of invention in mind,reference may be made to Fig. l in which is shown a Vacuum-tightcontainer I of conventional form in which is positioned an anode 2 and acontrol electrode 3 of conventional type. The container I may beevacuated to the highest vacuum attainable but my invention will befound to be well adapted for use in discharge tubes inwhich a gaseousatmosphere of appreciable pressure, such, for example, as mercury vapor,neon or argon is present.

The electrical-discharge device l is provided with a cathode 4 whichconsists of a thin ribbon, preferably of a high-resistance metal, whichis bent back and forth on itself or pleated in the manner indicated inthe drawing to form a pill.- rality of planes in the major portion ofits surface. A specific material which I-have found to be desirable isthe alloy of cobalt,,nickel and ferrotitanium, commonly known by thetrade-mark name Konel, and described and claimed in my copendingapplication Serial No. 144,911 filed October 28, 1926 and assigned tothe Westinghouse Electric & Manufacturing Company. The pleated ribbonjust described is preferably bent into the form of a cylinder, asindicated in Fig. 1, and is supported at its two ends on two rigidinleading wires 5 and 6 sealed through the wall of the container I.

After being pleated and bent to approximately its final form, thecathode ribbon may be coated over its entire surface, except at the endswhich are attached to the inleading wires 5 and B, by a material adaptedto emit electrons freely when heated. A mixture of equal parts of bariumoxide and strontium oxide made into a paste by moistening with bariumnitrate and painted and dried on the cathode ribbon is one example of anelectron-emissive coating suitable for my cathode. The ribbon thuscoated may then be welded to the inleading wires 5 and 6, which havebeen previously mounted in the press but which have not been sealed inplace therein. The stem, with the cathode thus attached, may then besealed into the containing bulb, and the tube thus formed exhausted andprovided with the desired gaseous atmosphere by methods well known inthe lamp art.

It is usually desirable that the cathode shall operate with acomparatively small potential difference between its ends and it will bereadily apparent that materials having a proper resistivity areavailable so that the cathode which I have described will so operate. Itwill likewise be apparent that the pleating or multiple-folding of thecathode renders it more rigid and better adapted to support itself byreason of the corrugations thus introduced into its structure. It may,in certain instances, be desirable to bridge across the adjacent ends ofsuccessive folds of the metal by means of high-resistance struts, whichmay be of silica or of some high-resistance alloy of small diameter inorder to provide a mechanically strong construction.

It will also be recognized that the bending of the pleated ribbon into acylindrical form is desirable, though not necessary, and that, forcertain purposes, it may be more desirable to form the pleated ribboninto a different shape. For example, Fig. 3 shows a cathode comprising apleated ribbon which is disposed in a straight line between itssupports, a grid electrode and a plate anode being disposed to surroundthe cathode thus formed, The, mode of operation is believed to be tooobvious to require any extended description.

Instead of coating the cathode ribbon with barium and strontium oxides,in the manner above described, it may be desirable to make the ribbonitself from an alloy which embodies electronemissive substancesincorporated within it. Thus, alloys of nickel and metallic barium maybe employed to constitute the cathode, these having the property ofemitting electrons freely when heated. Such cathodes are, however, notbeing claimed in this application, but are described and claimed in myjoint application Serial No. 404,196 with G. B. Halliwell, filedNovember 1, 1929 and assigned to the Westinghouse Electric &Manufacturing Company. Another form of cathode which will be founduseful in the present connection consists of a ribbon of the alloydesignated by the trade name Konel on which has been deposited a surfacelayer containing metallic barium. This may be done by placing the k0nel"Within an exhausted container where it will come into contact with theheated vapor of barium trinitride. The form of electron-emissive cathodejust described is also described and claimed in my copending applicationSerial No. 424,745, filed January 30, 1930 and assigned to theWestinghouse Electric & Manufacturing Company.

When a cobalt-nickel base alloy is employed as the core material, theelectron-emitting metal is in intimate contact or bond with the basemetal and is, at least partially, alloyed therewith.

Cathodes prepared in the manner specified are considerably superior toplatinum filaments coated with an alkaline-earth metal because they givesatisfactory emission at a lower temperature, are less expensive, andhave considerably longer life in service. In fact, theirelectronemissive propetries compare favorably with oxidecoatedfilaments. Such filaments may be readily and uniformly reproduced,however, and are not subject to the other inherent defects which arecharacteristics of oxide coated filaments.

The alloy which I employ has a base or core metal containing nickel andcobalt in the aggregate of to in which the nickel and cobalt are presentin proportions ranging from 95% to 5% nickel and from 5% to 95% cobalt,the remainder of the alloy consisting of iron and an additionalingredient which is effective in increasing the strength of the alloy,such as tungsten, manganese, titanium, vanadium or molybdenum. Theadditional ingredient is preferably added in the form of a ferrousalloy, the total amount of which must be maintained below 30%. Theadditional ingredient constitutes from /3 to A1 of the ferrous alloy sothat its content will not exceed 10% of the final material.

While the proportionsabove specified have been stated broadly, thenickel is preferably maintained in excess of the cobalt because nickelis less susceptible tooxidation than cobalt and, at the present time, isless expensive. I have found that the alloys known under the trade-markKonel which contain cobalt, nickel, iron and titanium are especiallysuitable, and particularly the alloy containing 80 parts nickel, 20parts cobalt and 7 parts iron and /2 parts titanium.

It will be evident that, if desired, the cathode ribbon above describedmay not itself constitute the heating element but that it may beemployed as an enclosure or wall about an independent heater of am!convenient form from which it may be wholly or partially insulated. Itwill also be recognized that the articulation of the cathode surface maybe effected otherwise than by pleating a plane ribbon as hereindescribed. Thus, if desired, cross walls between the pleats dividing thecathode into a series of nearly closed chambers will be found to be adesirable .construction .for certain purposes. The presence of anappreciable pressure of gas in the container is found to preventspace-charge effects from producing a high internal impedance, inthecase of cathodes having convoluted surfaces, such as are here described.By reason of the fact that the convolutions or chambers are nearlyclosed, the angle between their sides being less than a right angle,most energy radiated from any one area of a chamber wall strikes someother portion of the chamber wall and is there either absorbed orreflected. When a relatively small portion of the radiant energy takesthe direction of the open end of the chamber and is thus dissipated'tothe space surrounding the cathode, the cathode walls, under theseconditions, may be described as introspective. As is well known, theheat radiation in the interior of a nearly enclosed chamber isblack-body radiation.

The electrons in Fig. 1 travel through the space between the cathode 4and anode 2. The aver- Due to the area of the deep pleats in thecathode, the area of the cathode is many times the area of this averagecross sectional area.

One of the principal advantages of the oathode which I have heredescribed is that the heat dissipation to the surrounding surfaces isminimized and that, consequently, the amount of heating energy requiredto maintain them in a condition capable of emitting an electron currentof large magnitude is relatively small. In order to further this effect,it may be desirable to wholly or partially surround the cathodes byreflecting walls or by walls which are heat insulated. The current whichflows from anode to cathode must, of course, traverse the'body of thecathode ribbon and its heating eiTect therein may be very appreciable.In certain instances, it may, in fact, be suchthat, once the tube isstarted in operation, all other heating current for the cathode may bedispensed with. The provision of reflecting and heat-insulatingenclosures of the cathode will assist in producing this result.

In certain instances, it may be found desirable to position the anodewholly or partially within an enclosure comprising the cathode surface.For example, the anode may occupy the center of a cylindrical cathode,such as that illustrated in Fig. 1.

In accordance with the patent statutes, I have described particularembodiments of my invention, but it will be recognized that these areintended to be illustrative only and that the broad principle thereofwill be capableof alternative embodiments which will be evident to thoseskilled in the art. I desire, accordingly, that the claim shall be giventhe broadest construction of which its terms are susceptible in view ofthe prior art.

I claim as my invention:

An electrical-discharge device having a gaseous atmosphere andcomprising an anode and a substantially annular cathode of closelypleated sheet metal coated with an electron emissive layer, the anglebetween the sides of successive pleats being less than ninety degrees.

ERWIN F. LOWRY.

